Sub-irrigated planters (SIP) are simple devices that allow low-maintenance, low-water consumption container gardening.
A simple SIP has three major parts:
- a container for soil;
- a container for water; and
- a wick that allows water to be drawn from the water container into the soil container.
The wick (typically made of fabric or polyester) draws water up into the soil through capillary action, where the plant roots absorb it at an appropriate rate for the plant.
Aeration holes in the soil container, combined with overflow holes in the water container, help prevent the soil from becoming too wet (which may cause the plant roots to rot.)
This diagram shows the major parts of a simple SIP made from a plastic pop bottle.
SIPs can be easily constructed from a variety of readily available (and commonly discarded containers) using simple tools. Commonly made sizes range from 1 liter pop-bottle SIPs to 50 liter-plus SIPs made from plastic storage totes.
For instructions on making SIPs visit: http://web.archive.org/web/20121104163540/http://www.scribd.com/doc/35818333/DIY-Two-Bucket-EarthBox-Sub-Irrigated-Planter http://suresimple.blogspot.com/2009/04/recycling-juice-and-pop-bottles-as-sips.html http://www.globalbuckets.org/
5-Gallon SIP Instructions
It all starts with providing a water reservoir at the bottom of your container. You can do this either by nesting two containers together (the top one holds soil, the bottom one water), or by making some kind of divider that sits toward the bottom of a single container and holds the soil above the reservoir. However you construct it, the barrier between the soil and water should be full of small holes for ventilation.
The water is pulled up from the reservoir and into the soil by means of something called a wicking chamber. This can be a perforated tube, a basket, a cup or anything full of holes that links the soil to the water. The soil in the chamber(s) becomes saturated, and it feeds moisture to the rest of the soil.
The reservoir is refilled by means of a pipe that passes through the soil compartment down to the very bottom of the container.
The last essential element is a hole drilled into the side of the container at the highest point of the reservoir. This is an overflow hole that prevents you from oversaturating your plants.
2 food-grade, 5-gallon plastic buckets. If possible, one of them should have a lid. 1 16-ounce plastic drink cup, or a 32-ounce plastic yogurt container, or anything similar that you can punch holes in. A plastic bucket of similar size would work, too. 1 bucket lid (can substitute a plastic garbage bag in a pinch) Plastic twist ties 17 inches of 1-inch-diameter PVC pipe, copper tubing, a bamboo tube or anything similar A big bag of potting mix
Drill, Keyhole saw, safety knife or saber saw
- Find two food-grade, 5-gallon plastic buckets. A good source is behind restaurants and doughnut shops. If they once held food, you know they aren't going to be toxic (but do wash them). Don't source your buckets off of construction sites!
- Cut a hole right in the center of the bottom of one of the buckets. The yogurt container or whatever you are using is going to sit in this hole, so it hangs down into the water reservoir below (the bottom bucket), and act as your wicking chamber. Do this by tracing an outline of the cup on the bottom of the bucket, and then cutting a little inside the line. Use a safety knife, or a keyhole saw for this. It doesn't have to be pretty.
All you have to make sure of is that your wicking chamber will fit in that lower bucket. If the chamber is too tall, you won't be able to fit the two buckets together. This is something that is easy to adjust as you go, but just keep it in mind from the beginning.
To give you an idea of sizes, we have one SWC made from two five-gallon Kikkoman soy sauce buckets. For that one the wicking chamber is a 32-ounce yogurt container, and it hangs down 3 1/2 inches into the reservoir.
- Cut another hole in the bottom of the same container, anywhere near the outside edge (anywhere but the center). This hole is for the pipe that will refill the reservoir and should be sized accordingly. Again, just trace around one end of your pipe and cut.
- Now drill a bunch of 1/4-inch holes in the remaining real estate on the bottom of this same bucket. The exact number or spacing does not matter; these are ventilation holes. Go for a Swiss cheese effect, but don't get too carried away. Leave the other bucket intact.
- Now turn to your wicking chamber — the drink cup or yogurt container. Punch or drill a bunch of random 1/2-inch holes all over the sides of the cup, but not the bottom (the soil would fall out if the bottom were open). These big holes will allow water to seep into the soil in the chamber and thus be drawn into the soil above.
- Attach the wicking chamber to the bottom of the top bucket. This is a very loose affair, consisting of four twist ties. Just drill holes at the 12, 3, 6 and 9 o'clock positions just below the top edge of the cup, and drill corresponding holes near the edge of the large hole you cut in the middle of the bucket. Thread plastic twist ties through these holes to secure the wicking chamber so that it hangs beneath the holey bucket.
- If necessary, cut the pipe that feeds the reservoir to a good length. You want it to poke out of the top of the container for easy watering. Seventeen inches is just about right for this project. Cut one end of the tube on the diagonal, and put this end down in the bucket. The angled end will allow water to flow freely out of the tube and into the reservoir.
- Place the bucket fitted with the suspended wicking chamber into the untouched bucket.
- Make your overflow hole. Figure out where the bottom of the top bucket sits in relation to the bottom bucket. Try holding it up to strong light, or employing a ruler. Drill a 1/4-inch hole in the side of the lower bucket (the previously untouched bucket), placing the hole just a little beneath the bottom edge of the inside bucket. This hole will serve to spill off overflow from the reservoir chamber. You want the top bucket to be wicking water, not sitting in water.
10. Finally, insert the watering pipe through the hole you drilled in the bottom of the inner bucket. Be sure to put the pointy end in the bucket. The flat end will stick out the top.
11. Fill your new container with potting mix. Note that you must use potting mix because regular garden soil doesn't work very well in SWCs. Fill the container all the way to the top, moistening the soil as you go.
12. Plant your plant, dead center.
13. Make a circular, shallow trough around the perimeter of the plant, and sprinkle about a cup dry organic fertilizer in the trench. Then cover the trench up with a little soil so the fertilizer is just slightly buried — don't work the fertilizer into the soil. You must be careful with fertilizers and SWCs because they are closed systems. Excess fertilizer doesn't drain away. So always keep it at the top off the container, where it will work its way down gradually.
14. If you've got a lid for the bucket, and your plant is small enough, go ahead and cut a hole in the center of the lid for the plant to poke through, then ease the lid into place, threading the plant's leaves through the hole. The lid will help retain moisture. If you don't have a lid, or if your plant is too big, cut an X in a plastic garbage bag and lay it across the top of the pot, securing it around the sides with a length of tape or string, or if you have a lid for the bucket, you can cut out the center and use the rim to secure the plastic.